The craniovertebral junction (CVJ), which is composed of the distal third of the clivus, the occiput, the atlas, the axis, and the foramen magnum, is complex anatomically and includes important neurovascular structures1,2. Together, these structures enclose the cervicomedullary junction (CMJ) and the lower four cranial nerves. Signs and symptoms of abnormal conditions affecting the CVJ are varied and typically begin insidiously. They may be referable to the brainstem, cervical cord, cerebellum, cervical nerve roots, or lower cranial nerves or the vascular supply to these structures. Anterior compression at the CVJ can occur in many types of abnormalities: malformations (basilar invagination or cranial settling, atlas assimilation, os odontoideum, and atlantoaxial fixed dislocation), tumor, trauma, chronic inflammatory diseases (most frequently, rheumatoid arthritis [RA]), and osteomyelitis3-7. Not uncommonly, congenital ventral compression of the CVJ is discovered on postmortem examination8.
We present an unusual case of anterior CVJ compression in a healthy woman due to hyperplasia of the clivus with horizontal segmentation and degeneration of the atlanto-occipital and atlantoaxial joints. The presenting symptoms were suggestive of carpal tunnel syndrome. The patient was informed that the data concerning the case would be submitted for publication, and she provided consent.
A forty-two-year-old female school bus driver presented to our neurology clinic with bilateral upper-arm, forearm, and hand numbness and tingling, which she had experienced for two years; the left side was more symptomatic than the right. She had minimally impaired sensation in the thumb and index finger of the left hand. Deep tendon reflexes were intact bilaterally. Physical examination demonstrated positive Phalen and Tinel signs over the carpal tunnel bilaterally. An electrophysiology study revealed mild demyelination in the left distal median nerve and notable demyelination in the right distal median nerve consistent with bilateral carpal tunnel syndrome.
Subsequently, the patient was seen in the orthopaedic clinic, because of pain in both upper extremities and hands as well as pain in the posterior occipital and upper cervical region, which had developed over the prior two months without any preceding traumatic event. The neck pain was intermittent, was worse in the morning, and was precipitated by neck flexion. Walking had become more difficult, particularly on uneven surfaces. The pain in the arms was intermittent, and she described it as cramping and numbness. She also complained of dysphagia, with liquids more than solids, which had worsened over the preceding two months. In addition, she described a shocklike sensation, which extended into all four extremities, that most typically occurred when she drove over bumps in the road or with neck flexion. On examination, the pupils were of equal size, round, and reactive to light bilaterally. Her face was symmetric, her tongue was midline, and extraocular motions were all intact. Sensation was intact in the fifth cranial nerve distribution. Motor strength was 5 of 5 with good tone and bulk in all four extremities. Her reflexes were hyperreflexic symmetrically in all four extremities, and she had bilaterally positive Hoffmann reflexes. The examination showed normal results for the Romberg and Babinski tests, a normal heel-toe gait, and no clonus.
Radiographic analysis demonstrated cervicomedullary compression (Fig. 1). The tip of the odontoid process was in the Clark station1,9. Measurements related to the Chamberlain line, McGregor line, clivus-canal angle, and the Redlund-Johnell scale were normal and did not reveal upward migration of the odontoid process or occipital hypoplasia or hyperplasia10-13. The unique features of the magnetic resonance imaging (MRI) and computed tomography (CT) scans were a horizontal cleft of the clivus, clivus hypertrophy, fibrous periodontoid pannus, and pseudoarticulation between the clivus and the odontoid process (Figs. 2 and 3). A rheumatologic work-up was performed. The erythrocyte sedimentation rate (ESR) was 14 mm/hr (normal, <20 mm/hr), testing for the rheumatoid factor was negative, and there was no small-joint involvement. The patient had a positive (diffuse) homogeneous antinuclear antibody (ANA) titer, typically associated with systemic lupus erythematosus and mixed connective-tissue disease, but the cause of this finding was unknown.
Because of the progressive symptoms, surgery was recommended. The patient underwent endoscopic endonasal decompression with excision of the hypertrophied clivus, the anterior arch of the atlas, and the odontoid process14. The spine was then stabilized with a C1-C2 arthrodesis and bone-grafting from the posterior approach. The preoperative symptoms of tingling, numbness, and cramping in the arms resolved by postoperative day 1. On postoperative day 2, repeat imaging showed adequate decompression of the CMJ with stable atlantoaxial fixation (Fig. 4). Four weeks after surgery, the patient was walking without support and had motor strength of 5 of 5 in the upper and lower extremities.
In a large series of ninety individuals with proatlas segmentation abnormalities, Menezes and Fenoy8 reported that 85% to 90% of patients presented between the first and second decades of life (age range, three to twenty-three years). The anomalies reported were basioccipital hypoplasia, condylar hypoplasia and hyperplasia, and atlanto-occipital assimilation. To the best of our knowledge, neither clivus hyperplasia nor basioccipital hyperplasia has been described in the literature. We hypothesize that the reason for the CVJ anomaly in our patient was a failure of fusion of the synchondrosis at the basiocciput and basisphenoid, leading to abnormal motion and resulting in clivus hyperplasia. We are aware of only one other reported case of a living adult patient with myelopathy due to a congenital abnormality of the CVJ, but this resulted from a defect in the development of the proatlas as opposed to a failure of fusion of the clivus15.
Many radiographic features with which to evaluate the CVJ have been described15. We analyzed various radiographic parameters, but none of them were abnormal. The entity of clivus hyperplasia is uniquely important and re-emphasizes the fact that none of the radiographic parameters truly describe this abnormality of the CVJ.
Among the acquired adult causes of CVJ abnormality, RA is the most frequent16. Synovial hypertrophy with villous fronds (i.e., pannus formation) results from humoral mediators and principal inflammatory cells. Eventually, there is destruction of articular cartilage and bone, along with the development of synovial cysts and ligamentous laxity17. RA has a unique propensity to adversely affect the complex joints of the upper cervical spine. Due to the complexity of these joints and their corresponding articular surfaces, substantial arthropathy with ligament, joint, and bone destruction can occur. Atlantoaxial instability results from involvement of the transverse ligament. Similarly, basilar invagination results from involvement of the alar ligaments, the occipital condyles, and the odontoid process18-20. The presence of pannus is a characteristic feature of RA; the presence of soft tissue in the periodontoid region raised the possibility of RA in our case. However, a normal ESR as well as the absence of small-joint involvement, serum rheumatoid factor, and bone erosions at the CVJ suggested otherwise. The only other remaining possibility was an osteoarthritic degeneration of the CVJ. It is possible that, as can happen in other areas of the spine, increased motion and instability due to clivus hyperplasia and segmentation led to early degeneration of the CVJ with formation of fibrous periodontoid pannus in this particular patient.
In 1974, Taylor and Byrnes21 reported that extramedullary compression of the CMJ in monkeys resulted in venous stasis of the gray matter in the lower cervical spinal cord segments21. This could possibly explain the false localizing symptoms and signs of lower cervical cord involvement with the actual pathologic condition of the craniocervical junction. Likewise, the complex decussation that takes place in the cervical spinal cord at the level of the foramen magnum can result in a false sense of localizations in the lower cervical cord in patients presenting with central cord syndrome22,23. This could explain the symptoms that suggested carpal tunnel syndrome in our patient at the initial presentation.
In summary, careful analysis of radiographic findings in our case demonstrated some unique features. The presence of clivus hyperplasia and cleft with the absence of radiographic parameters of basilar invagination, plus the presence of fibrous periodontoid soft tissue, make this case rare. The presence of the odontoid process articulation with the basiocciput in the absence of atlantoaxial joint instability seen on flexion and extension views suggests that it is a complex deformity. The abnormal shape of the clivus articulated with the odontoid process anteriorly and formed a pseudojoint, even in the presence of a normal occipitoatlantal articulation. The inflammation and motion at this pseudarthrosis led to the formation of a fibrous pannus, which contributed to the constriction observed at the CMJ.